(a) Field of the Invention
The present invention relates to a carbon-based composite particle for an electron emission display device and a method for preparing the same, and, more particularly, to a carbon-based composite particle having a high level of electron emission and a method for preparing the same.
(b) Description of the Related Art
Earlier field emission displays (hereinafter referred to as “FED”) were made of a spindt-type electron emission source including Mo or Si, with sharp tips of sub-micron size. Since the spindt-type electron emission source is assembled with sharp tips of a sub-micron size, the method of fabricating the same requires a great deal of attention, and such an operation is considered high-level precision work. Therefore, it is difficult and expensive to produce a large-sized field emission display device according to this method.
Carbon material has recently emerged as a potentially useful electron emission source due to its low work function. One carbon material, a carbon nanotube (CNT), is particularly expected to be an ideal electron emission source since it features a high aspect ratio and a small tip radius of curvature of 100 Å, and thereby electrons are readily emitted by applying an external voltage of as low as 1˜3 V/μm.
Generally, the electron emission source is fabricated in such a manner that the carbon nanotubes are formed in a paste with a solvent, a resin, and so on, the paste is applied between substrates by a screen-printing method, and then it is sintered. Since the carbon nanotubes have a low work function, the resultant electron emission source can be driven by applying low voltages, and the method of fabricating the same is not complicated. It will thereby offer advantages for large size panel displays. However, when the electron emission source is produced with carbon nanotubes by the screen-printing method, each carbon nanotube is roughly mixed with a solid powder present in the paste and irregularly distributed in the solid powder, so that the tips of most of the carbon nanotubes are covered by the solid powder. In addition, most of carbon nanotubes are oriented in a direction parallel with the substrate instead of the direction perpendicular to the substrate which is where the electro-field is applied. Accordingly, the ratio of carbon nanotubes incapable of emitting electrons to all carbon nanotubes is increased so that the electron emission capabilities are not fully utilized. Generally, an electron emission cathode fabricated by such method has a planar shape so that the surface area is minimized.
Therefore, there are considerable demands to find a way to expose the tips of the carbon nanotubes. As one scheme to satisfy such demands, Korean laid-open patent publication No. 2000-74609 discloses that carbon nanotubes are admixed to metal powders. However, this method requires an additional process to expose and align the carbon nanotubes, rendering the process overly complicated. Further, it is difficult to align many carbon nanotubes perpendicularly, and only a few metal particles have been observed to have carbon nanotubes on the surface thereof.
Further, Japanese laid-open patent publication No. 2000-223004 discloses a method for exposing the carbon nanotubes in which carbon and the metal particulate are mixed and compacted, then the compacted mixture is cut and selectively etched. However, this method is also quite complicated and is difficult to apply to a field emission device of an electron emission array.
Moreover, Japanese laid-open patent publication No. 2000-36243 discloses a method in which a laser beam is irradiated on the surface of a printed pattern in which carbon nanotubes are covered with silver particles combined with a binder, and the silver particles and the binder present on the surface are selectively removed, so that the carbon nanotubes are exposed. However, such laser irradiation can tend to thermally damage the carbon nanotubes.